1. Field of the Invention
The invention relates to a hybrid vehicle (HV) and a control method therefor. More specifically, the invention relates to a hybrid vehicle equipped with a switch implementing switching between setting and canceling a fuel economy priority mode, in which priority is given to fuel efficiency, and a control method for such a hybrid vehicle.
2. Description of Related Art
A hybrid vehicle of this type has been suggested in which when the degradation degree of fuel supplied to an engine is determined to be high, the required load which is required for the engine is increased and the consumption of the fuel with a high degradation degree is enhanced (see, for example, Japanese Patent Application Publication No. 2009-255680 (JP 2009-255680 A)). In such a hybrid vehicle, where the fuel degradation degree is determined to be high in a motor drive mode in which the engine drive is stopped and the vehicle travels using power only from a motor, the engine is started and the consumption of the fuel with a high degradation degree is enhanced.
Further, it has also been suggested to make a transition to a fuel consumption enhancement mode in which the period in which the engine is driven is extended when the fuel supplied to the engine is determined to have degraded and the remaining amount of the fuel is equal to or higher than a threshold (see, for example, Japanese Patent Application Publication No. 2012-030668 (JP 2012-030668 A)). In such a hybrid vehicle, the degraded fuel is rapidly consumed due to the transition to the fuel consumption enhancement mode.
It has recently been suggested to provide a hybrid vehicle with a switch for setting a fuel economy priority mode in which priority is given to fuel efficiency as compared with the usual travel mode, or to give priority to a motor drive mode, in which the engine is not started till the battery is charged by electric power from an external electric power source and the cumulative capacity of the battery becomes sufficient to start the engine. In such hybrid vehicles, it should be determined how to handle the setting of the fuel economy priority mode when fuel degradation is determined.